The chairman of the Joint Chiefs of Staff told Congress Thursday he had no doubt that Russia was responsible for the bombing of a U.N. humanitarian aid convoy in Syria Monday.

America’s top military officer, Gen. Joseph Dunford, offered his opinion of who was behind the attack earlier this week on an aid convoy in Aleppo. “There is no doubt in my mind that the Russians were responsible,” he told Congress on Thursday morning.

Gen. Dunford also made it very clear that an order to cooperate with Russia in regard to Syria will not be followed by the military.

“The U.S. military role will not include intelligence sharing with the Russians,” Dunford said during the hearing on U.S. national security challenges and ongoing military operations. “I do not believe it would be a good idea to share intelligence with the Russians.”

The Obama administration’s agreement with Russia, announced on Sept. 9 by Secretary of State John Kerry and his Russian counterpart Sergey Lavrov, would involve the United States and Russia working together to develop military strikes against Nusrah, the al Qaeda affiliate in Syria, and the Islamic State given a sustained period of reduced violence. The United States and Russia also agreed to share information to establish a “Joint Implementation Center” to cooperate in targeting terror groups.

The planned cooperation between the United States and Russia has been subject to criticism, given Moscow’s goal of propping up Syrian President Bashar al-Assad and targeting of U.S.-backed rebels under the guise of combating ISIS.

“When I look at Russia’s nuclear capability, when I look at their cyber capability, when I look at their developments in undersea warfare, when I look at their patterns of operations—how often they’re operating, the locations they are operating in—these are kinds of operations that we haven’t seen in over 20 years,” Dunford said.

Gen. Dunford continued, “When I look at Mr. [Vladimir] Putin’s activities in Ukraine, in Crimea, in Georgia, that causes me to say that a combination of their behavior as well as their military capability … would cause me to believe that they pose the most significant challenge, potentially the most significant threat, to our national interests.”

With at least 400,000 people killed in Syria and millions displaced, the policies put forth by Obama’s administration was questioned during the hearing.